Internally expanding brake



Oct. 18, 1938.. .1. H. PRATT ET AL. 2,133,669

INTERNALLY EXPANDING BRAKE Filed April 20, 1937 2 Sheets-Sheet l Oeh 18,M J. H. PRATT ET AL H3569 .NTERNLLY EXPANDING BRAKE Filed April 20, 19372 Sheets-Sheet 2 /5/ f5@ 34 Fly. 4f, wg n l 75 Patented Oct. 18, 1938UNITED STATES PATENT OFFICE IN TERNALLY EXPANDING BRAKE James HenryPratt, Gilbert Edgar Manley, and

Albert Henry Godfrey Girling, Birmingham,` England Application April 20,1937, Serial No. 137,992 In Great Britain February 18, 1937 2 Claims.(Cl. 18S-78) This invention has reference to improvements to a block 3and one of the securing bolts 9 emrelating to internally expandingbrakes and has ployed for this purpose projects inwardly from for itsobject the provision of an improved brake the said block and has locatedaround a plain of this kind which provides for a more powerful portionof the shank thereof a bearing sleeve Ill 5; braking eiort thanheretofore without involving Which is normally held in frictionalcontact with 5 the use of a Servo motor and which inter alia theadjacent face of the block 8 by means of ensures equal Wearing of thebrake linings and a washer II and nut I2 said nut I2 engaging a enablesa relatively lighter drum to be employed threaded portion on the end ofthe said bolt 9. than with the constructions of internally ex- Thesleeve IE) serves as an abutment for the lo pending brakes heretofore inuse. upper ends 0f a pair O ODDOSitely arranged aCtLl- 19 The inventionconsists of an improved internating levers i3 the lower ends of whichabut ally expanding brake which incorporates four or oppositely movablethrust exerting members I 4 more brake shoes the combined length of theWhich can be moved outwardly when required arcs of which issubstantially equal to the cirfor expanding the brake by an expansionmechal5. cumference of the drum, said shoes being opponisin which willbe described in detail hereinsit-ely arranged and adapted for a limitedsliding after. Each actuating lever I3 col-operates with circumferentialmovement when the brake is apa pair of brake shoes I3a and I3b; I3C andI3Cl plied whereby a powerful self-energizing braking respectively andthese brake shoes carry on the eiort is provided. peripheries strips I5of material having a high 20 The invention further resides in animproved cio-efficient of friction the combined lengths of 20 brake ofthe internally expanding type having the said strips I6 beingsubstantially equal to four arcuate brake shoes the braking surface theinner circumference of the drum 6. The whereof extends substantiallycompletely around adjacent ends of the rearwardly presented shoes thecircumference of the brake drum said brake Ilia, I'Sb abut, likewise theadjacent ends of the 2,-) shoes being arranged in pairs and beingcapable forwardly presented shoes ISC, i3d, .and the 25 or" a limitedsliding movement relatively to the lower ends of the two shoes I3a, I3d(I0-Operate anchor plate and being operatively connected to with a iixedabutment I'IEL carried by the carrier a pair of actuating levers bymeans, preferably plate l' and a similar diametrically opposed abutaspring means, which permits both a circumferment Ilb is carried by theblock 8 for contact 3f) ential and also a rocking movement of the shoesby the upper ends of the upper shoes I3b, I3. 3o to obtain substantiallyabout the centres thereof. Each brake shoe I3a, I 3b, I 3c and I3d is ofan The invention still further resides in the deinverted U-shape incross section, see Figure 5, tails of construction of the improvedinternally with an internally disposed U-shaped bracket expanding braketo be described hereinafter. I3 which rests on the peripheries of a pairof 35 The invention will now be described with par- Centrally disposedrollers I9 mounted on a spin- 35 ticular reference to the accompanyingsheet of dle 2i) which passes through the respective acdrawings,whereinztuating lever i3. Pivoted to the centres of the Figure l is -apart sectional front elevation of actuating levers I3 are pins 2I whichserve as the improved internally expanding brake. pivots for springs 22,23 having curved ends m Figure 2 is a fragmentary view in sectionalwhich bear on side flanges I 82L of the respective 40 plan of theexpansion mechanism for the brake bearing brackets I8 and tend tomaintain the shoes. said bearing brackets I8 in Contact with the Figure1S a longitudinal Vetlcal 580151011 0f peripheries of the respectiverollers I9. The the brake lllustratedm Flgure 1 springs 22 and 23 tendto resist any tendency Figure 4 is a' fragmentary View Showing the ofthe shoes I3a, I3b, I3c and I3d to slide circumrlar ofietxpalsonlcflismd for ghe brake ferentially but readily permit of therocking of s Oesw e Co er p e Ove an the shoes. The brake actuatinglevers I3 are Fi ure 5 is a fragmentary view in section taken on mgmplane indicated by the une 5 5 Figure l. lnterconnected by means ofsprings 24 wh1ch tend O As illustrated in the drawings the improved t?mamtam .the Shoes 3a abi '3c amd 3d out l brake comprises a drum 5 whichis adapted to o1 Contact with the drum 6 said springs 24 bebe xed t0 thevehicle Wheel in known manner ing located on one side of the actuatinglevers so and a carrier plate 'I which carries the mechathat a Santingtendency iS introduced which IS nism now to be described and which isfixed t0 resisted by the contact of the shoes with raised 5 the vehicle.The carrier plate 1 has bolted thereportions Ia carried by the carrierplate l. 55

The brake actuating levers I3 are proportioned according to known tenetsto ensure exactly equal wear on the brake linings IS.

The thrust exerting members I4 are provided with screw threaded shankswhich engage with the tapped bores of sleeves 25 which are rotatablymounted within a housing Z6 secured to the carrier plate 1. At theirinner ends the sleeves 25 are provided with bevel teeth 252L which meshwith bevel teeth 21a carried by a. toothed annulus 21 having spur teeth2'Ib which mesh with teeth 2|!EL carried by a spindle 28 which isrotatably mounted in the housing 26 and which is adapted for rotation bymeans of a key applied to the shaped outer projecting, end of the saidspindle 28. Disposed within the inner ends of the sleeves 25 are blocks29 having inclined plane surfaces with which contact freely movablerollers 30 the diametrically opposite portions of which contact withcorrespondingly inclined plane surfaces carried by a wedge member 3|adapted to be actuated by a rod 32 in known manner.

The operation of the invention is as follows:-

Upon the application of the brake when the vehicle is moving in aforward direction due to the wedge member 3| being caused to move in aninward direction and, through the rollers 30, blocks 29, sleeves 25 andthrust exerting members I4, to effect an expansion of the actuatinglevers I3 against the resistance of the springs 24, the firstapplication of the brake results in the bearing sleeve I0 locatingitself relatively to the plain portion of the bolt 9 so as to centralizethe whole of the mechanism. The upper brake shoe I3b of the rearwardlypresented pair of brake shoes |32, I3b is pushed into contact with theabutment I'Ib by its complementary brake shoe |321, the lower brake shoeI3d of the forwardly presented pair of brake shoes I3, I3d being pushedinto contact with the abutment IIa by its complementary shoe |30. Thiscircumferential movement of the brake shoes adds a powerfulself-energizing braking effort to the braking effort provided by theexpansion of the actuating levers I3. A reverse circumferential movementof the brake shoes |33, I3b, |30, I3d takes place when the brakes areapplied with the Vehicle moving in a reverse direction in which case theopposite sides of the abutments I'IEL and I1b come into play.

It will be appreciated that the life of the brake linings I6 ismaterially increased over that of two brake shoe internally expandingbrakes by reason of the increased area of contact between the four brakeshoes |3a, |311, I3c and I3d and the drum 6.

It is found also that the short lengths of the arcs of the strips I6enables the whole of the frictional material to be utilized and theproportioning of the actuating levers I3 ensures equal wearing of thelining of all shoes so that more than twice the usable volume offrictional material is made use of than with ordinary two brake shoeinternally expanding brakes.

Furthermore, it is found that the even radial pressure exerted by thesubstantially continuous surface contacts eliminates drum distortion andpermits a lighter drum 6 to be used and also a higher ratio between thetravel of the drivers foot when operating the brake and the resultantmovement of the brake shoes for applying the brake.

Moreover, it is found that the rocking permitted to the shoes |33, |3b,I3C, I3d, about the central pivots provided by the rollers I9 equalizesthe pressure at each end of the shoes and reduces the amount ofclearance necessary to prevent rubbing or contact in the event of drumdistortion.

It will be appreciated that the actuating levers I3 are isolated fromany braking effort and serve merely to control the actuation of thebrake shoes..

We claim:-

l. An internal expanding brake comprising a brake drum, a relatively xedcarrier plate, a fixed projection carried by said plate, a sleeve ofgreater diameter disposed around said projection, a frictional means forresisting the movement of said sleeve, a pair of oppositely arrangedactuating levers mounted on said carrier plate having adjacent endsthereof in contact with the sleeve, an expansion means adapted to exerta thrust on the other adjacent ends of the actuating levers, rollerscarried by the actuating levers, brake shoes rockably mounted at theircentral portions on said rollers and capable of a circumferentialmovement relatively to said levers,

spring means anchored to each actuating lever for maintaining eachrespective pair of brake shoes in Contact with the rollers carried bysaid actuating levers and means for restoring the actuating levers tothe out of action position when the brake is released, the combinedlengths of the arcs of the arcuate brake shoes approximating tc thecircumference of the drum, said circumferential movement adding apowerful selienergizing braking effort to the braking effort provided bythe expanding means.

2. An internal expanding brake according to claim 1 wherein therestoring springs are arranged on one side of the actuating levers toproduce a canting effect and wherein fixed abutments are provided forresisting said canting.

JAMES HENRY PRATT. GILBERT EDGAR MANLEY. ALBERT HENRY GODFREY GIRLING.

